. Luteinizing hormone releasing hormone (LHRH) has found utility in suppressing serum testosterone to values found in surgically castrated patients. From a psychologic, social and even economic perspective, a longer-acting LHRH analog may be preferable to the irreversible alternative, surgical castration. A number of delivery systems have been evaluated and even marketed without, it is asserted, due consideration to the practical limitations to patient well-being that attend surgically implanted "rods" or solvent-containing microspheres. Based on recent pilot trials (in rats) using an active LHRH analog, it is proposed to investigate the potential for an injectable 90-day release system that could be delivered via a conventional hypodermic needle. It is asserted that such a system would offer the patient an acceptable alternative for suppressing serum testosterone. During Phase I, samples will be prepared, characterized, and evaluated in vitro followed by in vivo testing in rats. Phase II studies will focus on optimization of the formulation, with Phase III including preparation of material for initial clinical trials.